Showing papers by "Suljo Linic published in 2018"

Catalytic conversion of solar to chemical energy on plasmonic metal nanostructures

Abstract: The demonstrations of visible-light-driven chemical transformations on plasmonic metal nanostructures have led to the emergence of a new field in heterogeneous catalysis known as plasmonic catalysis The excitement surrounding plasmonic catalysis stems from the ability to use the excitation of energetic charge carriers (as opposed to heat) to drive surface chemistry This offers the opportunity to potentially discover new, more selective reaction pathways that cannot be accessed in temperature-driven catalysis In this Review, we provide a fundamental overview of plasmonic catalysis with emphasis on recent advancements in the field It is our objective to stress the importance of the underlying physical mechanisms at play in plasmonic catalysis and discuss possibilities and limitations in the field guided by these physical insights Plasmonic catalysis has recently revolutionized the field of catalysis, promising to achieve improved control over catalytic reactions by targeting specific electronic excitations In this Review, Linic and co-workers discuss the recent advances in the field, focusing on the underlying physical mechanisms and their application in catalysis, as well as limitations and future perspectives

Design Principles for Directing Energy and Energetic Charge Flow in Multicomponent Plasmonic Nanostructures

Abstract: The decay of localized surface plasmons supported by plasmonic metal nanoparticles results in the formation of energetic charge carriers within the nanoparticles. Once formed, these charge carriers can transfer to chemically attached materials where they can perform a function. The efficient extraction and utilization of these charge carriers in various applications hinges on the ability to design plasmonic nanostructures with highly localized charge carrier generation at specific locations in the nanostructure. Herein, we shed light on the physical mechanisms governing the flow of energy in resonantly excited multimetallic plasmonic nanoparticles. We demonstrate that coating plasmonic nanostructures with nonplasmonic metals can result in the preferential dissipation of energy (i.e., formation of charge carriers) in the nonplasmonic metal and that the extent of this dissipation depends heavily on the electronic structure of the constituent metals. We use experimental and modeling studies of various core–s...

Multicomponent Catalysts: Limitations and Prospects

Abstract: There has been a recent surge of interest in multicomponent catalysts that combine properties of chemically diverse materials. A major factor in this increased interest is the widespread recognition that the scaling relationships for adsorption and transition state energies of reactions place significant constraints on making step-change improvements in catalyst performance using monofunctional catalysts. In this perspective, we review the fundamental rationale for multicomponent materials and describe several classes of materials that offer promise for improving activity and selectivity in catalysis. Our focus is on illustrating how recent advances in the ability to prepare precisely controlled multicomponent nanostructures have the potential to enhance the capability to design highly active and selective catalysts.

Nanoscale Engineering of Efficient Oxygen Reduction Electrocatalysts By Tailoring the Local Chemical Environment of Pt Surface Sites

Abstract: The oxygen reduction reaction is the limiting half-reaction in hydrogen fuel cells. While Pt is the most active single component electrocatalyst for the reaction, it is hampered by high cost and low reaction rates. Most research to overcome these limitations has focused on Pt/3d alloys, which offer higher rates and lower cost. Herein, we have synthesized, characterized, and tested alloy materials belonging to a multilayer family of electrocatalysts. The multilayer alloy materials contain an AuCu alloy core of precise composition, surrounded by Au layers and covered by a catalytically active Pt surface layer. Their performance relative to that of the commercial Pt standards reaches up to 4 times improved area-specific activity. Characterization studies support the hypothesis that the activity improvement originates from a combination of Au–Pt ligand effects and local strain effects manipulated through the AuCu alloy core. The presented approach to control the strain and ligand effects in the synthesis of P...

In search of membrane-catalyst materials for oxidative coupling of methane: Performance and phase stability studies of gadolinium-doped barium cerate and the impact of Zr doping

Abstract: Oxidative coupling of methane (OCM) is a promising technology for the direct conversion of methane to ethylene and ethane (C2). This process is yet to be commercialized due its poor yield reflected in the formation of undesired products such as CO and CO2 (COx) as methane conversion increases, particularly in conventional packed bed reactors (PBRs). It has been argued that by applying O2− conducting membrane reactors that distribute the oxygen feed, the selectivity to the C2 products can be increased. A practical design for these membrane reactors would include combining a selective catalyst, preferably O2− conducting, with an O2− conducting membrane. In this work, we studied an O2− conducting material, gadolinium-doped barium cerate (BaCe0.8Gd0.2O3-δ or BCG), to evaluate its potential applicability as a catalyst and membrane in OCM membrane reactors. From PBR tests, we found that this material was active for OCM, and achieved a maximum C2+ yield of ∼14% at 1023 K. Furthermore, at low oxygen partial pressures, a C2+ selectivity of ∼90% was obtained at methane conversions of ∼3%. Although the C2+ yield from this material was stable over 48 h on stream at high methane conversions, X-ray diffraction data showed that the BCG perovskite phase, which is required for its conductive (membrane) properties, decomposes into BaCO3, CeO2 and Gd2O3 like phases, due to reactions with CO2. We showed that doping BCG with Zr was effective at suppressing the phase instability in OCM without significantly affecting the C2+ yields.

Maximizing Solar Water Splitting Performance by Nanoscopic Control of the Charge Carrier Fluxes across Semiconductor–Electrocatalyst Junctions

Abstract: Protective insulating layers between a semiconductor and an electrocatalyst enable otherwise unstable semiconductors to be used in photocatalytic water splitting. It is generally argued that in these systems the metal electrocatalyst must have work function properties that set a high inherent barrier height between the semiconductor and electrocatalyst and that the insulating layer should be as thin as possible. In this study we show that, for systems which suffer from inherently low barrier heights, the photovoltage can be significantly improved by tuning the thickness of the insulating layer. We demonstrate this in a case study of a system consisting of n-type silicon, a hafnium oxide protective layer (thickness 0–3 nm), and a Ni electrocatalyst. By optimizing the protective layer thickness, we observe increased efficiencies for photocatalytic oxygen evolution with a thick Ni electrocatalyst supported on n-Si. Our findings open avenues for the use of inexpensive electrocatalysts with favorable electroca...

Modeling the Impact of Metallic Plasmonic Resonators on the Solar Conversion Efficiencies of Semiconductor Photoelectrodes: When Does Introducing Buried Plasmonic Nanostructures Make Sense?

Abstract: It is well established that plasmonic nanoparticles embedded in a semiconductor can, under certain conditions, increase the rate of charge carrier collection in electrocatalysts bound to the semico...